1. Field of the Invention
The present invention relates to a continuously variable valve lift device for a vehicle, and more particularly, to a continuously variable valve lift device for a vehicle, which can vary the lift amount of valves according to engine operating state.
2. Description of Related Art
According to a general cam provided in a conventional engine, it is impossible to change a valve lift and duration. In addition, since it is required to fix a fixed valve lift and duration to a specified number of rotations, the fuel consumption ratio and output optimization cannot be sought.
Recently, in order to improve the fuel consumption ratio and output, attempts to vary the valve lift and an opening/closing period of intake/exhaust valves have been actively made, and one of devices developed as a part of such efforts is a continuously variable valve lift (CVVL) device.
That is, the continuously variable valve lift device can optimally control the valve operation such as the valve lift and the opening/closing period of the intake/exhaust valves in accordance with operational conditions of the engine. Specifically, the continuously variable lift device can maximize a flow rate of an intake air at high speed/high load requiring high output, and minimize an effect of EGR (Exhaust Gas Recirculation) or a loss of throttle at low speed/low load where it is important to improve the fuel consumption ratio or to reduce the exhaust gas.
According to the conventional variable valve lift device, however, an advance function is not provided, and due to a short a period where the intake valve and the exhaust vale overlap each other, the fuel consumption ratio can be improved only by applying the exhaust-side CVVT.
In addition, when the valve is lifted, an open duration becomes longer than a close duration to deteriorate the dynamic characteristics such as the acceleration characteristics and so on, and the valve duration is lengthened to lower the performance and the fuel consumption ratio.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.